Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium or intermediate transfer surface.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. A color printer typically uses four colors of ink (yellow, cyan, magenta, and black). These colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
Ink sticks of each color are delivered through corresponding feed channels to a melt plate. The key plate has keyed openings to aid the printer user in ensuring that only ink sticks of the proper formulation and color are inserted into each feed channel. Each keyed opening of the key plate has a unique shape. The ink sticks of the color for that feed channel have a shape corresponding to the shape of the keyed opening. The keyed openings and corresponding ink stick shapes exclude from each ink feed channel ink, sticks of all colors except the ink sticks of the proper color for that feed channel. Unique keying shapes for other factors are also being employed to exclude unintended sticks from being incorrectly inserted, including formulation and market or geographic pricing differences.
Ink sticks currently in use are typically manufactured with a formed tub and flow fill process. In this method, the component dyes and carrier composition are first compounded and then heated to a liquid state and poured into a tub having an interior shape corresponding to the desired finished ink stick shape. The result is an ink stick that, at room temperature, is typically a solid or semi-solid having a wax-like consistency. Colorant added to the ink composition can be a dye or pigment or combination, for simplification the term dye will be used.
The tub may also be formed with indentations and protrusions for forming keying and coding features in the ink sticks, if desired. These key elements are protuberances or indentations that are located in different positions on an ink stick. In some cases, the key elements are placed on different sides of ink sticks of different colors that are included in an ink stick set. This enables for detection and identification of the different ink sticks, particularly during loading, as noted above. For instance, corresponding keys on the perimeters of the openings through which the ink sticks are inserted into their appropriate feed channel exclude ink sticks of the set, particularly those of different colors, which do not have the appropriate perimeter key element.
Even with keying features, however, the incorrect identification and loading of ink sticks into the appropriate feed channel can be problematic. For instance, incorrect loading of the ink sticks generally occurs in one of two ways, either by loading the incorrect color and shaped ink stick in the incorrect key plate or by inserting the correctly colored ink stick incorrectly in the correct receptacle. One reason for this is that ink sticks may be so saturated with color dye that it may be difficult for a printer user to tell by color alone which color is which. Cyan, magenta, and black ink sticks in particular can be difficult to distinguish visually based on color or other appearance.
Moreover, if an ink stick is inadvertently inserted through the wrong opening in a key plate or if the correct ink stick is incorrectly oriented during insertion, the ink stick can be damaged and small pieces or particles of ink can be broken off the main ink stick body. Thus, while the keying features of an ink stick may work to prevent the wrong color ink stick from being inserted into a feed channel, the soft exterior surface of an ink stick may be damaged making the entire ink stick unusable as a result.
An ink stick is typically pushed or slid along the feed channel by the feed mechanism until it reaches the melt plate. An ink stick's waxy exterior surface generates friction as the ink stick is pushed along a feed channel. This friction may cause stick-slip movement of the ink stick and the ink stick may get skewed and hang up or catch within the feed channel. The friction encountered by an ink stick increases in proportion to the number of ink sticks that are in the feed channel and is significantly affected by the elevated environmental temperatures within the printing device.
Some provisions have been made to prevent the solid masses of shaped ink from sticking to surfaces of the feed chutes so that an unrestricted feed of ink sticks proceeds down the channel to the heater plate for melting. For instance, the feed channel and/or the ink stick may include cooperating alignment and orientation features that facilitate alignment of ink sticks in the feed channel so the possibility of jamming due to skewing of the ink stick is reduced. The areas on a typical ink stick for keying and guiding elements, however, are typically small. Simply increasing the size of a stick to accommodate additional features may not be beneficial because the lateral dimensions of the ink stick must not exceed constraining dimensions of the ink loader or printer.